This invention relates to a tool for extracting broken or damaged screws embedded in bone or wood. Pedicle screws are screws that are inserted into the pedicle of a human vertebra to secure a plate or the like to an adjacent vertebra. As with all screws, they may be damaged or broken during installation or through wear, requiring removal.
Prior art approaches to removal of damaged screws include using a plurality of sharp teeth in a tool to hold the metal of the screw while turning as shown in U.S. Pat. No. 2,750,821 to Hilsinger, a modified slotted blade with sharp leading edges as shown in U.S. Pat. No. 4,434,687 to Vickio or a tool that requires drilling a bore down the center of the damaged screw or bolt to receive a reverse threaded or fluted tool, commonly called an "easy-out" as shown in U.S. Pat. No. 1,547,944 to Murphree. U.S. Pat. No. 4,350,064 to Markle issued Sep. 21, 1982, shows a more recent approach in which an easy out is attachable to an electric drill or rachet wrench.
In medical applications, it may be very difficult to use an easy-out in that drilling a pilot hole generates metal filings which cannot be allowed to be left in the surgical site, especially in the vicinity of the spinal cord. A tool that will not require drilling and that would not generate metal fragments is highly desirable.
The art described in this section is not intended to constitute an admission that any patent, publication, or other information referred to herein is "prior art" with respect to this invention, unless specifically designated as such. In addition, this section should not be construed to mean that a search has been made or that no other pertinent information as defined in 37 C.F.R. .sctn. 1.56(a) exists.